The present invention relates generally to the method and corresponding structure thereof for spin welding a plastic insert into an opening in a plastic workpiece such as is defined by a protruding boss or a recessed cavity therein.
Problems may arise in the attachment of fasteners to structures which require a finished cosmetic surface. Such a structure might be found in the grill assembly of an automobile. The grill assembly must be attached to an underlying structure of the vehicle. However, the grill assembly generally cannot have fasteners extending therethrough as such fasteners will effect the cosmetic appearance of the assembly. As such, attempts have been made to add a boss to the reverse side of the grill assembly so as to allow for attachment of a stud which is used to secure the grill assembly to the vehicle.
A problem arises with the forming of a boss on the grill assembly such that if the material thicknesses of the boss and the grill assembly are not properly dimensioned, a corresponding depression or sink will occur on the cosmetic surface of the grill assembly. Because the wall thickness of the boss must be less than the wall thickness of the grill assembly to avoid the forming of a depression or sink, problems have been encountered as to how to attach a fastener to the boss. If the fasteners are threaded, the resulting stud can be quite heavy, thick and costly. It would be preferable to provide a stud which is appropriately sized for the assembly considering numerous studs would be used to retain the grill assembly on the vehicle.
Another problem that has arisen due to the requirement that the wall thickness of the boss be less than the wall thickness of the grill assembly is that there may not be enough material in the wall of the boss to properly attach the threads of the fastener thereto, thus requiring a need for additional material for engagement of the fastener.
There has also been encountered a problem of attaching a combination washer fluid reservoir with an extending fan guard to a sidewall of an engine compartment. Typically, a stud is ultrasonically welded into the reservoir to effectuate such an attachment. One of the problems with this method is that a leak can be formed between the reservoir and the cavity of the stud. As such the leak may result in accidentally draining the washer fluid reservoir. The ultrasonic welding of the stud to the reservoir also causes recycling problems should a leak occur because the stud cannot be easily separated from the reservoir.
A general object of the present invention is to provide a spin weld assembly for inserting and retaining a fastener in engagement with a plastic workpiece without creating or exacerbating defects on a cosmetic side of the workpiece.
Another object of the present invention is to have the wall thickness of a boss on the workpiece generally equal to or less than the thickness of the workpiece itself.
Yet another object of the present invention is to provide a fastener that is appropriately sized for the required attachment of workpieces.
Still another object of the present invention is to provide a plastic insert which provides the needed material for an appropriately sized fastener to engage with, while still allowing the wall thickness of the boss to be less than that of the workpiece.
Another object of the present invention is to provide a spin weld assembly for inserting and retaining a fastener in engagement with a plastic workpiece that prevents a leak from being formed between the workpiece and the cavity of the fastener.
Yet another object of the present invention is to provide an insert that is spin welded into a boss or cavity of a workpiece such that the material effected by the spin welding and that forms a tight bond with the insert is displaced from the workpiece such that there is little or no effect on the workpiece.
Another object of the present invention is to provide a fastener that can be easily removed from the workpiece should there be a leak in the workpiece, thereby allowing the material in the workpiece to be recycled.
Still another object of the present invention is that the inserts of the spin weld assembly can be installed on the molded workpiece as necessary away from the molding machine thereby increasing the efficiency and speed of the molding machine and therefore reducing the cost.
Yet another object of the present invention is to provide a vent in the insert, boss or recess thereby allowing any air which is trapped between the insert and the inside surface of the boss or cavity during the spin welding to escape therethrough.
Briefly, and in accordance with the foregoing, the present invention provides novel structures for spin weld assemblies and a method for forming same. The spin weld assemblies are formed by attaching a fastener to a plastic insert which is then attached to a plastic workpiece. The fastener can take the form of many different structures, preferably a stud or a nut. The fastener is formed with a drive for driving the fastener into a bore of the plastic insert having first and second ends. Self-tapping threads on the fastener engage the fastener with the plastic insert when the fastener is driven into the bore of the insert. The insert, having the fastener threadedly engaged thereto, is then rotated and generally axially displaced into an opening of the plastic workpiece, thereby spin welding the insert to the workpiece. The first end of the insert provides proper alignment for the insert to be spin welded into the opening as the diameter of the first end is smaller than that of the opening. The second end of the insert provides the intimate engaging contact between the insert and a wall that defines the opening when the insert is spin welded into the opening as the diameter of the second end is larger than the diameter of the opening.